1. Field of the Invention
The present invention relates to an air tube for tires, to a process and related apparatus for its manufacture, and to wheels comprising tires provided with such an air tube; more particularly, the invention relates to an air tube intended for supporting the tire even in case of deflation thereof, as a result of a puncture for example.
More specifically, even if not exclusively, the air tube of the present invention is particularly suitable for tires of an elliptical transverse section in which the size of the minor axis parallel to the equatorial plane is smaller than the size of the major axis parallel to the rotation axis, and still more particularly for the so-called xe2x80x9clow-section tiresxe2x80x9d, in which the ratio of the section height measured between the bead base and the tread band centre to the maximum tire width is equal to or lower than 0.7.
2. Description of Related Art
For better understanding the terminology used in he progress of the present specification the main features of a tire are hereinafter briefly set forth.
Generally, a tire comprises a carcass of toroidal shape having a crown portion and two axially opposite sidewalls, terminating with a pair of beads, each provided with at least one bead ring for anchoring of the tire to a corresponding mounting rim, a tread band disposed crownwise to said carcass, the carcass being provided with at least one reinforcing ply extending from the bead to bead and having its ends anchored to said bead rings.
In the case of radial tires, a belt structure, interposed between the carcass and tread band is also present, which bead structure may be comprised of two superposed layers of metallic cords disposed in crossed relationship with respect to each other and a radially outermost layer having textile cords directed parallelly to the equatorial plane of the tire.
These tires delimit an inner space between the carcass and rim which can be directly filled with air under pressure or occupied by an air tube of rubber material inflated with air under pressure.
In connection with the different solutions adopted, tires are identified as tubeless tires or tube type tires.
Many and varied solutions have already been provided for enabling tire running even in the case of partial or complete loss of air, as a result of punctures for example, over a fairly long length, at a moderate speed, to allow reaching of a service area where the necessary repairs or replacements can be carried out. These punctures mostly take place due to nails or other sharp pointed bodies spread on the ground, although these are not the only causes for possible deflation.
As regards tires provided with an air tube, the most widely proposed solutions contemplate use of an air tube divided into a plurality of circumferential or transverse compartments, independent of each other, by means of walls disposed parallel or perpendicular to the equatorial plane of the air tube itself.
The presence of several compartments independent of each other enables a sufficient inflation pressure to be maintained in the tire, thereby allowing the tire to run in an emergency condition even when one of said compartments has been punctured.
Examples of such a kind of tire are disclosed in U.S. Pat. No. 2,039,343 and GB 2 104 012, wherein one or more partition wall divide the the air-tube into two or more annular chambers. Reinforcement of each partition wall is provided for assuring suitable resistance to puncturing agents. However, suitable measures are necessarily taken for allowing the partition wall to spread itself, so as to be forced into engagement with the sidewall of the tube when the air within one chamber expand, as a consequence of deflation of the other chamber upon failure caused by a puncturing agent.
FR 2 524 849 discloses an apparatus for manufacturing an air tube of conventional type, i.e. not provided with partition walls, said apparatus comprising a pair of cheeks and a male die removably interposed therebetween. An elastomeric compound is injected into two distinct cavities defined between each cheek and the male die interposed therebetween, so as to form two parts of the air tube. The male die is then removed and the cheeks are approached one to the other to form the air tube by joining the two parts at their opposite edges.
As regards tubeless tires, the proposed solutions have directed their efforts towards modifications of the carcass structure by either strengthening the tire sidewalls to make the tire capable of self-support or, alternatively, creating independent compartments similar to those of the air tubes.
On the contrary, the solution of leaving the xe2x80x9ctubelessxe2x80x9d version in favour of the xe2x80x9ctube typexe2x80x9d version is not feasible with the so-called low-section tires, that is those having elliptical sections increasingly more elongated relative to the rotation axis, in which a great difficulty is found in employing known rubber air tubes.
Actually, traditional air tubes during inflation take a substantially circular profile in right section which badly matches with the elliptical tire profile, giving rise to folds overlapping each other that make it impossible to reach a correct and complete extension of the air tube walls over the inner surface of the toroidal cavity, in particular at the tire sidewalls, thereby generating a bad filling of the toroidal cavity and a dangerous state of inner stresses in the air tube wall, so that the air tube becomes quickly useless.
Consequently, in low-section tires, devoid of an air tube, the problem of ensuring a run under emergency conditions is now still solved by modifying the carcass structure, as previously stated.
The utility model DE 296 20 713 U1 discloses a tubeless tire comprising an inner central vertical wall disposed between the centre line of the tread band and the wheel rim on which the tire beads are mounted. The vertical wall is fitted, at the lower end thereof, into an appropriate rim seat so as to define two air spaces inside the tire, which air spaces are independent of each other, and each of which is inflated by a respective valve.
Practically the principle which informs this solution corresponds to that of having two twin tires mounted on one and the same rim.
Should one of the two carcass parts be punctured, the tire will be stabilized by the air pressure existing in the other part located at the side of the deflated one.
Patent application FR 2,605,269, in turn, discloses a tubeless tire formed of a plurality of distinct circumferential compartments, disposed axially in side by side relationship.
An appropriate inflating device comprises a tube passing through the lower part of all partitions generating the different circumferential compartments and is provided with a hole at each compartment: fitted in the tube is an axially drilled rod provided, on its side wall, with other holes which can be brought into communication with those of the tube to enable inflation of the tire by air inflated from the rod. Axial displacement of the rod relative to the tube enables the holes of the former to be made offset relative to those of the latter so as to stop air escape from the different compartments.
In conclusion, there is not yet the availability of an air tube adapted for being used with a low-section tire, which is capable of ensuring running under emergency conditions without being obliged to resort to an expensive and complicated modification of the tire carcass structure.
The Applicant has perceived the possibility of solving the problem by adopting an air tube divided into at least two distinct circumferential portions, separated from, each other by a longitudinal wall, while however assigning a greater rigidity to said wall and preferably also to the area surrounding it than the axially outermost portion thereof, that is the air tube sidewalls, in such a manner that during inflation of the air tube inside the tire the air tube expansion in an axial direction is greater than that in a radial direction, so as to bring its central portion into contact with the tread area simultaneously with the complete lying down of the tube sidewalls against the tire sidewalls, while avoiding arising of abnormal stresses within the air tube walls.
The Applicant has further perceived that such a solution could be obtained by manufacturing the air tube sidewalls separately from the central portion thereof and subsequently joining the distinct portions to each other, conveniently by chemical adhesion of the respective elastomer materials during the air tube vulcanization.
In one aspect, the invention therefore relates to an air tube of elastomer material, which air tube is divided into at least two distinct circumferential portions, separated by an internal wall extend in a plane normal to the rotation axis of said air tube, having its ends joined to a pair of axially opposite sides that, together with said wall, delimit said distinct circumferential portions, characterized in that the rigidity of said wall is greater than that of the sidewalls.
Preferably, said air tube is characterized in that it comprises a central core and two axially opposite sidewalls, the core being formed of said wall provided at its ends with two flanges extending perpendicularly to the wall itself in axially opposite directions, the ends of which are associated with the corresponding ends of said sidewalls, the core rigidity being greater than that of the sidewalls.
In the following of the present description the air tube features, the method and apparatus for manufacturing said air tube as well as use of same in matching relationship with a tire are, for convenience, always described with reference to the core, but it is intended that they also apply when the core consists of the wall alone, substantially devoid of said flanges.
In accordance with a first embodiment, the different rigidity between the core and sidewalls is obtained by resorting to one and the same elastomer material and varying the core geometry relative to the sidewall geometry, and more particularly by making the core of a greater thickness than the sidewalls.
In accordance with a second embodiment, the different rigidity is achieved by adopting different materials having the same thickness, and more particularly through the use of a material of greater modulus for the core than for the sidewalls.
In an alternative solution, the different rigidity is obtained by adopting different materials and different thicknesses; in the embodiments providing different materials, preferentially the material of the central core is reinforced with short fibres in the form of pulp, of the type obtained by grinding processes.
In a second aspect, the invention relates to a tire wheel comprising a tube-type tire mounted on the corresponding rim.
The tire comprises a carcass of toroidal shape having a crown portion and two axially opposite sidewalls, a tread band located crownwise to said carcass and a belt structure disposed crownwise between the carcass and tread band; in a preferred embodiment of said tire the sidewalls terminate with a pair of beads incorporating bead rings for anchoring of the tire to said rim and, still more preferably, the carcass is provided with at least one reinforcing ply extending from bead to bead, having its ends anchored to said rings.
The air tube is divided into at least two circumferential portions separated by a wall extending in a plane perpendicular to the rotation axis of the air tube.
The lyre wheel is characterized in that said air tube comprises a central core ad two sidewalls; preferably the core, the rigidity of which is greater than that of the sidewalls, can have said wall provided with two flanges issuing from its ends and extending at right angles thereto in opposite directions over a length of predetermined width.
In a preferential solution the flange and sidewall ends are associated with each other by vulcanization.
In a preferential embodiment of the invention the tire wheel comprises said air tube inserted into a tire having a section ratio H/C not exceeding 0.7.
Preferably, the junction area between the radially outer flange of the central core and the corresponding air tune sidewall is axially internal to the corresponding end of the tire belt structure.
In a further aspect, the air tube of the invention is used as a vulcanization bladder, thus becoming one body with the tire carcass, in such a manner that it advantageously replaces the impermeable liner of tubeless tires.
In a third aspect, the invention relates to a process for manufacturing an air tube of elastomer material, divided into at least two distinct circumferential portions separated by an interior wall extending in a plane normal to the rotation axis of said air tube, characterized in that it comprises the following steps:
a) moulding a pair of sidewalls, separated from each other, for said air tube;
b) moulding said wall of the air tube in an annular configuration comprising a central core from the ends of which two flanges, i.e. a radially external one and a radially internal one, issue, said flanges extending axially in opposite directions at right angles to said core, over a length of predetermined width;
c) introducing said wall and sidewalls into one and the same vulcanization mould, said sidewalls being disposed with their opposite ends coaxial with each other and mutually facing, said wall being disposed between said opposite sidewall ends at a coaxial position with the sidewalls, and the flange ends and the corresponding sidewall ends being in mutual contact;
d) feeding fluid under pressure to a preestablished temperature into the different distinct portions of said air tube;
e) vulcanizing the air tube while at the same time causing a junction between said flanges and sidewalls.
Preferentially the process is put into practice by executing said moulding operations by injection of the elastomer material into cavities suitably arranged for formation of said sidewalls and wall.
In a fourth aspect, the invention relates to a mould for manufacturing an air tube of elastomer material, divided into at least two distinct circumferential portions, separated by a wall extending in a plane normal to the rotation axis of said air tube, characterized in that it comprises the following pieces:
a pair of axially external cheeks provided, at their mutually facing surfaces, with an annular cavity coaxial with the rotation axis of the air tube being formed, of a substantially semicircular right section;
a pair of axially intermediate male dies which are provided:
at their axially outer surfaces, with a first annular ridge coaxial with said rotation axis, of semicircular right section, housed, when the mould is closed, in the corresponding annular cavity of the adjacent cheek, the radius of said annular ridge being smaller than the radius of the corresponding cavity so as to delimit, in mating relationship with said cavity, a hollow space of a width corresponding to a sidewall of said air tube, and at their axially inner surfaces, with a second annular ridge coaxial with said rotation axis, in axial alignment with said first annular ridge, having a right section of substantially quadrangular shape, the maximum radial sizes of said first and second annular ridges being substantially identical; and
a pair of axially inner spacers, a radially inner disc and a racially outer concentric ring respectively, coaxial with said rotation axis, the disc having a smaller diameter than the radially inner diameter of the ring, the disc diameter and the radially inner diameter of the ring corresponding to the diameters of the radially inner and outer edges respectively of the cavities present in the cheeks, the thicknesses of said spacers being greater than the sum of the axial sizes of said second annular ridges, mating of said spacers with said adjacent intermediate male dies giving rise to a hollow space therebetween which corresponds to the shape of said wall of the air tube having an annular configuration comprising a central core, determined by the mutual axial distance between said second annular ridges, and two flanges, a radially external one and a radially internal one, issuing from the corresponding ends of said core, axially extended in opposite directions, perpendicularly to said core and of a geometric configuration determined by the radial distance between said second ridges and spacers;
said pieces being mutually removable with respect to each other.